M-3120 004 Beckhoff
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The Beckhoff M-3120 004 is part of the M Parallel IO Modules series and supports four encoder channels with A, B, and C signal types, including their inverted pairs. It features a 24-bit binary counter, a supply voltage of 24 VDC, and a limiting frequency of 1 MHz. The module provides data interface through II/O-Lightbus and has dimensions of 170 by 76 by 68 mm.
Internal Product Review
The M-3120 004 is a Beckhoff parallel I/O encoder counter module with 4 encoder channels and a II/O-Lightbus data interface. Fast 0.1 ms input delay and 1 MHz limiting frequency support accurate high-speed signal acquisition in motion feedback applications. Selectable 1x/2x/4x quadrature evaluation makes this module a strong choice for precise 24-bit binary counting.
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Product Description:
The M-3120 004 parallel I/O module is produced by Beckhoff for the M Parallel I/O Modules series. In a Lightbus network, this unit connects high-resolution position encoders to a controller, allowing binary counts to be registered and forwarded without additional signal conditioning. By consolidating multiple incremental channels inside one housing, the module simplifies wiring and supports deterministic motion sequences in distributed automation cells. It is intended for cabinet installation and operates from the same 24 VDC control supply used by typical Beckhoff bus couplers.
The module accepts a supply of 24 VDC (±10%) and draws only 0.1 A, so it can share compact power supplies with other Lightbus participants. Communication with the host PLC is through the I/O-Lightbus backplane at a 2.5 MBaud transfer rate, which sets the maximum refresh period for the 24-bit process images. The physical size is 170 × 76 × 68 mm, enabling installation on 35 mm DIN rail without exceeding standard cabinet depths. Internally, a 24-bit binary counter per channel records incremental pulses, and the counter can be disabled by a 24 VDC inhibit line that sinks 10 mA when active. A zero-pulse latch with 24-bit depth captures reference marks for homing routines, and quadrature evaluation can be set to 1×, 2×, or 4× multiplication to match the required resolution.
Upstream encoder signals are accepted up to 1 MHz, so high-speed servo feedback is not limited by the module. Four independent channels handle A, A(inv), B, B(inv), C, and C(inv) tracks, so the unit supports 4 incremental encoders with complementary outputs. The encoders are powered directly from the unit, which provides 5 VDC / 15 VDC selectable supply rails at up to 1 A total. Input stages introduce only 0.1 ms of delay, preserving tight phase alignment for motion control. A dedicated 24 V disable input is available to blank counters during index search sequences.
